Mechanical assemblies often use fasteners and typically blind rivets to secure one or more components together in a permanent construction. Blind rivets are preferred where the operator cannot see the blind side of the workpiece for instance where the rivet is used to secure a secondary component to a hollow box section. Also they are preferred where a high volume of assemblies are being produced as there are advantages to be gained from increased assembly speeds and productivity compared with say threaded or bolted joints.
One of the disadvantages of a blind rivet setting and again instancing a setting to a hollow box section is that the blind side set end of the rivet cannot be visually inspected for a correctly completed joint. This is especially relevant where there are a number of blind rivets used and these are of a multiplicity of different sizes both in diameters and lengths. Also there could be occasions where assembly operators are inexperienced or if the arrangements of rivets are complex or where rivets are incorrectly installed or perhaps not installed at all. To inspect assemblies after completion is not only expensive and unproductive and in some instances it is virtually impossible to identify if the correct rivet has been used in a particular hole.
A further consideration can be that modern assembly plants are using increasing numbers of automation rivet placement and setting machines where there is an absence of the operator.
The current monitoring of a rivet during the setting process has been limited to the use of two current methods. The first method employs the use of a hydraulic pressure transducer which measures working fluid pressure within the tool. This current method is limited to use in detecting fluid pressure alone. The second method uses a “load cell” mounted linear to the tool housing. This option is considerably larger in size and has limited field capability as a result. Typically, the second method additionally uses a LVDT to measure the translations of the various moving components. It is, therefore, an object of the present invention to provide a system that will continually monitor the setting process, the numbers of rivets set and the correctness of setting and to identify if there are small but unacceptable variations in rivet body length or application thickness. Also because assembly speeds are increasing it is an advantage to identify incorrect setting almost immediately instead of a relatively long delay where complex analysis of rivet setting curves are used. Other fasteners such as blind rivet nuts (POPnuts), self drilling self tapping screws or even specialty fasteners such as POPbolts can be monitored but for the purposes of this invention blind rivets are referred to as being typical of fasteners used with this monitoring system.